This application is based on Japanese Patent Application Nos. 2000-273135 filed Sep. 8, 2000 and 2001-064043 filed Mar. 7, 2001, the contents of which are incorporated hereinto by reference in their entireties.
1. Field of the Invention
The present invention generally relates to a vibration-damping device installed in a vibrative member of a vehicle, for reducing or attenuating vibration of the vibrative member. More particularly, the present invention is concerned with such a vibration-damping device which is novel in construction and which is suitably applicable to vibrative members of an automotive vehicle, such as a suspension member, a sub frame, a body panel, a mounting bracket, and a vibrative member or members used in an engine unit or an exhaustion system, so that the vibration-damping device exhibits an excellent damping effect with respect to vibrations excited in these vibrative members.
2. Description of the Related Art
As vibration-damping devices for damping or reducing vibration excited in vehicles such as an automotive vehicle, there are known (a) a mass damper wherein a mass member is fixed to a vibrative member, (b) a dynamic damper wherein a mass member is supported by and connected to the vibrative member via a spring member and (c) a damping material which is a sheet-shaped elastic member and secured to the vibrative member. However, these conventional devices suffer from various potential problems. For instance, the mass damper and the dynamic damper both require a relatively large mass of the mass member, and exhibit desired vibration damping effect with respect only to a considerably narrow frequency range. The damping material requires a relatively large space for its installation, and tends to be large in its weight. In addition, the dynamic damper and the damping material both suffer from difficulty in stably exhibiting desired damping effects thereof, since the damping effects of the dynamic damper and the damping material are prone to vary depending upon the ambient temperature.
The present applicant has been disclosed in International Publication No. WO 00/14429 a novel vibration damper used for an automotive vehicle, which includes a housing member having an inner space and fixed to the vibrative member, and an independent mass member which is disposed within in the inner space of the housing member with a spacing therebetween, without being bonded to the housing member, so that the independent mass member is displaceable or movable relative to the housing member. When vibrations excited in the vibrative member is applied to the vibration damper, the independent mass member and the housing member are brought into impact against each other at their elastic abutting surfaces, thereby exhibiting an vibration damping effect on the basis of loss or dissipation of vibration energy caused by sliding friction generated between the elastic abutting surfaces of the independent mass member and the housing member and caused by collision or impact of the independent mass member against the housing member. This proposed vibration damper is capable of exhibiting a high damping effect over a relatively wide frequency range of input vibrations, while assuring a relatively small mass of the independent mass member.
Extensive studies of the vibration damper disclosed in the International Publication No. WO 00/14429 by the inventors of the present invention, have revealed that the vibration damping effects of the vibration damper can be remarkably improved with respect to a specific frequency vibration by adjusting a mass of the independent mass member or a spring stiffness of the elastic abutting surface of the independent mass member and/or the housing member, for example. This might be considered as follows, according to an examination into frequency characteristics of the damping effect of the vibration damper conducted by the inventors. Namely, the impact of the independent mass member on the housing member in a vibration input direction causes a reciprocating displacement of the independent mass member relative to the housing member within the housing member. The reciprocating displacement of the independent mass member relative to the housing member due to the impact of the mass member on the housing member might exhibit an effect like resonance.
However, it is difficult to tune the vibration damper to exhibit an excellent damping effect with respect to a desired frequency vibration, owing to the resonance-like effect of the reciprocating displacement of the independent mass member. That is, tuning of the vibration damper is limited by several conditions. For instance, a size of the independent mass member is limited by a given space for installation of the vibration damper in the vehicle, while a lower limit of the spring stiffness of the elastic abutting surface of the independent mass member and/or the housing member is predetermined to ensure a desired durability of the elastic abutting surface. In particular, when a vibration to be damped has a low frequency, there are needed a relatively large mass of the mass member and a relatively small spring stiffness of the elastic abutting surface, for example. In this case, a desired tuning of the vibration damper is significantly difficult, whereby the conventional vibration damper is insufficient in its vibration damping effect with respect to vibrations within a low frequency band.
It is therefore an object of this invention to provide a vibration-damping device for a vehicle which is novel in construction and which permits sufficient durability of abutting portions of a mass member and a vibrative member, while ensuring sufficiently small spring stiffness generated in abutting portions upon impact of the mass member on the vibrative member. The vibration-damping device is easily tunable to exhibit an excellent damping effect owing to impact of the mass member on the vibrative member, with respect to input vibrations especially within a lower frequency band.
The above object may be attained according to the following modes of the invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the present invention is not limited to the following modes or combinations of technical features, but may otherwise be recognized based on the thought of the present invention that described in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A vibration-damping device for damping vibrations of a vibrative member of a vehicle, comprising: a mass member disposed in the vibrative member such that the mass member is non-adhesive to and is displaceable independent of and relative to the vibrative member, the mass member and the vibrative member being brought into impact against each other at respective abutting portions thereof, at least one of the abutting portions of the mass member and the vibrative member being formed of an elastic member adapted to undergo shear deformation due to a load applied thereto in a direction in which the mass member and the vibrative member are brought into impact against each other.
In the vibration-damping device constructed according to this mode (1) of the invention, when the mass member is forced to move into and impact on the vibrative member due to vibrations excited in the vibrative member, the elastic member defining at least one of the abutting portions of the mass member and the vibrative member undergoes shear deformation. Thus, upon impact of the mass member on the vibrative member, the spring constant generated in the abutting portions of the mass member and the vibrative member can be made smaller, in comparison with the case where the elastic member is formed to undergo compression deformation upon impact of the mass member and the vibrative member. Namely, the spring constant generated in the abutting portions of the mass member and the vibrative member can be decreased without changing of elastic properties or elastic characteristics of the elastic member.
This arrangement makes it possible to tune the vibration-damping device so that the reciprocating displacement of the mass member relative to the vibrative member due to the impact of the mass member on the vibrative member exhibits its resonance-like effect in the lower frequency band, without requiring an enlargement of the mass member and without deteriorating durability of the elastic member. Thus, the vibration-damping device of this mode (1) of the invention can exhibit an excellent vibration damping effect with respect to vibrations over a wide frequency range, i.e., ranging from at around 10 Hz to 100 Hz or more, which vibrations are prone to be excited in an automotive vehicle.
Described in detail, the vibration-damping device constructed according to the mode (1) of the invention is arranged such that at least one of the abutting portions of the mass member and the vibrative member is formed to undergo shear deformation when the mass member and the vibrative member are brought into impact against each other at the abutting portions. This arrangement ensures sufficiently large amplitude of the reciprocating displacement of the mass member relative to the vibrative member, owing to the resonance-like effect of the reciprocating displacement of the mass member relative to the vibrative member, even in the case where a low frequency vibration having a relatively small vibration energy is applied to the vibration-damping device. That is, the presence of the abutting portion formed of the elastic member formed to undergo shear deformation facilitates a bouncing displacement of the mass member relative to the vibrative member. For instance, the mass member is able to bounce off the vibrative member even in the case where vibrations to be damped excited in the vibrative member has an acceleration of not greater than 1 G (a gravity acceleration). Therefore, the vibration-damping device of this mode (1) of the invention can exhibit a desired damping effect based on the impacts of the mass member on the vibrative member, with respect to small energy vibrations such as vibrations likely to be excited in the vibrative member of the vehicle.
In this mode (1) of the invention, a material of the mass member is not particularly limited, but may be preferably selected from metallic materials such as steel, so that the mass member has a required amount of mass with a relatively small size. A material of the elastic member defining the abutting portion of at least one of the mass member and the vibrative member may preferably be selected from a group consisting of a rubber elastic body, elastomers, foamed bodies of rubber or elastomers, and the like, for example.
(2) A vibration-damping device according to the above-indicated mode (1), further comprising: a rigid housing having a hollow structure and being fixedly formed in the vibrative member, the housing defining a hollow space therein and the mass member being accommodated within the hollow space with a spacing therebetween such that the mass member is non-adhesive to and is displaceable independent of and relative to the housing, the housing partially defined by the elastic member to provide an abutting portion of the housing on which the mass member is brought into impact.
In this mode (2), the use of the rigid housing having the hollow structure makes it possible to apply the vibration-damping device of the present invention to any vibrative members, irrespective of configurations of the vibrative members. Namely, the use of the housing ensures impact of the mass member and the housing at their abutting portions, irrespective of the configuration of the vibrative member. It is appreciated that since the housing is fixedly disposed in the vibrative member, the abutting portion of the housing functions as the abutting portion of the vibrative member.
The housing may be formed integrally with the vibrative member, or alternatively be formed independently of the vibrative member. In the former case, the housing is partially or entirely formed by utilizing a part of the vibrative member. In the later case, the housing is formed by another member independent of the vibrative member, and is fixed to the vibrative member. The number of mass member installed within the hollow space of the housing is not particularly limited, but may be suitably determined taken into account the size or shape of the hollow space of the housing, the mass of the vibrative member, the magnitude of vibrations to be damped and the like. That is, the housing may accommodate a single mass member, or may otherwise accommodate a plurality of mass members. The configuration of the hollow space of the housing is not particularly limited, but may be selected from a cylindrical shape, a rectangular shape, a polygonal shape, or other various kinds of shapes, for example. The configuration of the mass member may be suitably determined depending upon configuration of the hollow space of the housing, and may be selected from a solid or a hollow spherical shape, a rod shape, a plate shape or other various shapes.
(3) A vibration-damping device according to the above-indicated mode (2), wherein the mass member is mainly formed of a metallic material, and the housing having an inner surface covered with an elastic layer formed integrally with the elastic member. This arrangement makes it possible to provide the mass member which is large in mass and compact in size, and assures an elimination of a need for covering the mass member with an elastic layer, while permitting a reduction or an attenuation of noises caused by the impact of the mass member on the housing.
(4) A vibration-damping device according to the above-indicated mode (2) or (3), wherein the mass member comprises a plurality of mass members which are independent of each other and which have respective masses different from each other. This mode (4) of the invention facilitates to tune the plurality of mass members so as to have respective resonance frequencies of their reciprocating displacement relative to the housing. Thus, the vibration-damping device according to this mode (4) is able to exhibit a high damping effect with respect to vibrations within a plurality of frequency bands or over a wide frequency band, e.g., vibrations likely to be excited in the vehicle, such as engine shakes, engine idling vibrations and booming noises.
(5) A vibration-damping device according to any one of the above-indicated modes (2)-(4), wherein the mass member comprises a plurality of mass members which are independent of each other, and the housing comprises a plurality of the abutting portions on which the plurality of mass members are brought into impact, respectively, each of the plurality of the abutting portions of the housing including a first abutting part which is formed of the elastic member, the abutting parts formed of the elastic members on which the plurality of mass members are brought into impact, respectively, having different spring constants.
According to this mode (5) of the invention, the reciprocating displacements of the plurality of mass members can be easily tuned to exhibits their resonance effects with respect to different frequency bands, like in the vibration-damping device constructed according to the above-indicated mode (4). Therefore, the vibration-damping device of this mode (5) is capable of exhibiting an excellent vibration damping effect with respect to vibrations within a plurality of frequency bands or over a wide frequency band.
According to the invention, each mass member is desirably arranged to have a mass within a range of 10-1000 g, preferably 50-500 g as measured in a single body thereof. With the mass of the mass member set to 1000 g or smaller, more preferably 500 g or smaller, the mass member is prone to be excited to make its bouncing movement or displacement with ease and efficiency, upon application of the vibrational load to the vibration-damping device. With the mass of the mass member set to 10 g or larger, more preferably 50 g or larger, the vibration-damping device ensures its damping effect based on the impact of the mass member on the vibrative member.
To ensure the excellent damping effect of the vibration-damping device of the invention, the mass member is preferably arranged to be reciprocally displaceable by a distance within a range of 0.1-1.6 mm, more preferably within a range of 0.1-1.0 mm, between a first and a second abutting parts of the abutting portion of the vibrative member, which are opposed to each other in a direction in which vibrations is applied to the device. Since the range of reciprocating displacement of the mass member is held within such a significantly small length, the mass member is likely to impact against the vibrative member at opposite sides of the vibration input direction, even when the vibrations excited in the vehicle, which generally has a small amplitude, are applied to the vibration-damping device. This arrangement ensures a further excellent damping effect of the vibration-damping device with respect to the vibrations excited in the automotive vehicle.
According to the present invention, the abutting portions of the mass member and the vibrative member do not need to be formed entirely of the elastic member which undergoes shear deformation upon application of a load in a direction in which the mass member and the vibrative member impact against each other, but at least one of primary abutting parts which are opposed to each other in a direction in which a low frequency vibrations to be damped is applied to the device, may be formed of the elastic member. Preferably, the abutting portion of at least one of the mass member and the vibrative member may be entirely covered with an elastic layer, such as a rubber layer to thereby effectively preventing or reducing noises caused by the impact of the mass member on the vibrative member.
In this respect, the elastic member which at least partially constitutes the abutting portion of the mass member and/or the vibrative member, may preferably has a Shore D hardness of 80 or lower, more preferably, within a range of 20-40, as measured in accordance with ASTM method D 2240. For the above-mentioned improved damping effect and the reduced impact noise, the abutting portion of the mass member and/or the vibrative member is also arranged to have a modulus of elasticity within a range of 1-104 MPa, more preferably, 1-103 MPa, and a loss tangent is not less than 10xe2x88x923, more preferably within a range of 0.01-10.
According to the present invention, a mass of the mass member is held within a range of 5-10% of a mass of the vibrative member, preferably. Namely, if the mass of the mass member is smaller than 5% of the mass of the vibrative member, the vibration-damping device possibly suffers from difficulty in exhibiting a desired damping effect, and if the mass of the mass member is larger than 10% of the mass of the vibrative member, the vibration-damping device suffers from a problem of increase in the overall weight of the device. If the plurality of vibration-damping devices are installed in the vibrative member, the total mass of the plurality of mass members is desirably arranged to be held within a range of 5-10% of the mass of the vibrative member.